This article provides both a diachronic and synchronic account of the generalization of perfective auxiliary BE in specific irrealis modal contexts across numerous Romance varieties spoken in Italy and more widely within the Romània, which has essentially gone unnoticed in the descriptive and theoretical literature. In some cases (southern Calabrian, Latin American Spanish, Portuguese), the distribution of BE is to be interpreted as a residue of an original unaccusative syntax which was exceptionally preserved under higher V-movement in irrealis contexts, whereas in others (person-driven dialects of central and southern Italy, southern peninsular Spanish, Romanian) this original unaccusative signal has been reanalysed as a specialized marker of irrealis (lexicalizing a high Mood head) and extended to all verb classes. In the case of Alguerès, by contrast, the generalization of irrealis BE is argued to be the result of language contact with surrounding Sardinian dialects where a specific pattern of dedicated irrealis marking of Mood° has been replicated. Finally, the reverse pattern with generalization of irrealis HAVE, the reanalysis of an aspectual distinction between resultative and experiential perfects found in early Romance varieties (Neapolitan, Sicilian, Spanish, Catalan), is shown to involve a similar pattern of dedicated irrealis marking in Mood°.